///////////////////////////////////////////////////////////////////////////
//                   __                _      _   ________               //
//                  / /   ____  ____ _(_)____/ | / / ____/               //
//                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
//                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
//               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
//                           /____/                                      //
//                                                                       //
//               The Next Generation Logic Library                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////
//                                                                       //
//  Copyright 2015-20xx Christoph Zengler                                //
//                                                                       //
//  Licensed under the Apache License, Version 2.0 (the "License");      //
//  you may not use this file except in compliance with the License.     //
//  You may obtain a copy of the License at                              //
//                                                                       //
//  http://www.apache.org/licenses/LICENSE-2.0                           //
//                                                                       //
//  Unless required by applicable law or agreed to in writing, software  //
//  distributed under the License is distributed on an "AS IS" BASIS,    //
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
//  implied.  See the License for the specific language governing        //
//  permissions and limitations under the License.                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

package org.logicng.transformations;

import org.logicng.formulas.And;
import org.logicng.formulas.Equivalence;
import org.logicng.formulas.Formula;
import org.logicng.formulas.FormulaFactory;
import org.logicng.formulas.FormulaTransformation;
import org.logicng.formulas.Implication;
import org.logicng.formulas.Not;
import org.logicng.formulas.Or;
import org.logicng.formulas.cache.PredicateCacheEntry;

import java.util.LinkedHashSet;

import static org.logicng.formulas.cache.TransformationCacheEntry.AIG;

/**
 * And-inverter-graph (AIG) transformation.  Returns the AIG of the given formula.
 * @version 1.0
 * @since 1.0
 */
public final class AIGTransformation implements FormulaTransformation {

  private FormulaFactory f;
  private boolean cache;

  @Override
  public Formula apply(final Formula formula, boolean cache) {
    this.f = formula.factory();
    this.cache = cache;
    switch (formula.type()) {
      case FALSE:
      case TRUE:
      case LITERAL:
        return formula;
      case NOT:
        return transformNot((Not) formula);
      case IMPL:
        return transformImplication((Implication) formula);
      case EQUIV:
        return transformEquivalence((Equivalence) formula);
      case AND:
        return transformAnd((And) formula);
      case OR:
        return transformOr((Or) formula);
      case PBC:
        return apply(formula.cnf(), cache);
      default:
        throw new IllegalArgumentException("Could not process the formula type " + formula.type());
    }
  }

  private Formula transformNot(final Not not) {
    Formula aig = not.transformationCacheEntry(AIG);
    if (aig == null) {
      aig = f.not(apply(not.operand(), cache));
      if (cache) {
        not.setTransformationCacheEntry(AIG, aig);
        aig.setPredicateCacheEntry(PredicateCacheEntry.IS_AIG, true);
      }
    }
    return aig;
  }

  private Formula transformImplication(final Implication impl) {
    Formula aig = impl.transformationCacheEntry(AIG);
    if (aig == null) {
      aig = f.not(f.and(apply(impl.left(), cache), f.not(apply(impl.right(), cache))));
      if (cache) {
        impl.setTransformationCacheEntry(AIG, aig);
        aig.setPredicateCacheEntry(PredicateCacheEntry.IS_AIG, true);
      }
    }
    return aig;
  }

  private Formula transformEquivalence(final Equivalence equiv) {
    Formula aig = equiv.transformationCacheEntry(AIG);
    if (aig == null) {
      aig = f.and(f.not(f.and(apply(equiv.left(), cache), f.not(apply(equiv.right(), cache)))),
              f.not(f.and(f.not(equiv.left()), equiv.right())));
      if (cache) {
        equiv.setTransformationCacheEntry(AIG, aig);
        aig.setPredicateCacheEntry(PredicateCacheEntry.IS_AIG, true);
      }
    }
    return aig;
  }

  private Formula transformAnd(final And and) {
    Formula aig = and.transformationCacheEntry(AIG);
    if (aig == null) {
      final LinkedHashSet<Formula> nops = new LinkedHashSet<>(and.numberOfOperands());
      for (final Formula op : and)
        nops.add(apply(op, cache));
      aig = f.and(nops);
      if (cache) {
        and.setTransformationCacheEntry(AIG, aig);
        aig.setPredicateCacheEntry(PredicateCacheEntry.IS_AIG, true);
      }
    }
    return aig;
  }

  private Formula transformOr(final Or or) {
    Formula aig = or.transformationCacheEntry(AIG);
    if (aig == null) {
      final LinkedHashSet<Formula> nops = new LinkedHashSet<>(or.numberOfOperands());
      for (final Formula op : or)
        nops.add(f.not(apply(op, cache)));
      aig = f.not(f.and(nops));
      if (cache) {
        or.setTransformationCacheEntry(AIG, aig);
        aig.setPredicateCacheEntry(PredicateCacheEntry.IS_AIG, true);
      }
    }
    return aig;
  }

  @Override
  public String toString() {
    return this.getClass().getSimpleName();
  }
}
